Looks like the best you can do with your current PSU is a 7600GT. The 17amps on your 12V rail are barely enough for the 7600GT, and probably wouldn't be enough for the comparable ATI solution the X1650XT.
the op could always get a new PSU. A good choice would be the FSP AX450 for $58. Might have an issue though with the mobo connector for older mobos. Look into that